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		<h1 id="pagetop">EHCI debugging on the BeagleBone Black</h1>

			<p><a href="index.html">Back to previous index</a></p>
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	<div class="section">
		<h1>EHCI debugging</h1>
		<ol class="toc">
			<li><a href="#FindUSBportonthetargetthatsupportsEHCIdebug">Find
					USB port on the target that supports EHCI debug</a></li>
			<li><a href="#InitialsetupofBBBtoactasEHCIdebugdongle">Initial
					setup of BBB to act as EHCI debug dongle</a></li>
			<li><a href="#PatchBBBsgdbgpmoduleoptionalbuthighlyrecommended">Patch
					BBB's <tt>g_dbgp</tt> module (optional, but highly recommended)</a></li>
			<li><a href="#ConfigurelibrebootwithEHCIdebug">Configure
					libreboot with EHCI debug</a>
				<ol>
					<li><a href="#SelectingHCDIndexandUSBDebugport">Selecting
							<tt>HCD Index</tt> and <tt>USB Debug port</tt></a></li>
				</ol></li>
			<li><a href="#Howtogetthedebuglogs">How to get the debug
					logs</a></li>
			<li><a
				href="#EnebleEHCIDebugonthetargetskerneloptionalrecommended">Eneble
					EHCI Debug on the target's kernel (optional, recommended)</a></li>
			<li><a href="#References">References</a></li>
		</ol>
		<p>If your computer does not boot after installing libreboot, it is
			very useful to get debug logs from it, from the payload (grub) and/or
			the kernel (if gets to there). All of them stream debug logs on the
			available serial (RS-232) by default. However, most of todays laptops
			lack RS-232 port. The other option is to stream the logs to USB EHCI
			debug port.</p>
		<p>This section explains step-by-step how to setup BBB as a
			&#8220;USB EHCI debug dongle&#8221; and configure libreboot and the
			linux kernel to stream logs to it (TODO: grub).</p>
		<p>I will refer to three computers:</p>
		<ul>
			<li><b>host</b> - this is the computer you use, have
				tools, compiler, Internet, etc</li>
			<li><b>BBB</b> - Beaglebone Black (rev. B or higher, i
				use rev. C)</li>
			<li><b>target</b> - the computer you are trying to
				install liberboot</li>
		</ul>
		<h3 id="FindUSBportonthetargetthatsupportsEHCIdebug">Find USB port
			on the target that supports EHCI debug</h3>
		<p>
			Not all USB controllers support EHCI debug (see: <a
				href="http://www.coreboot.org/EHCI_Debug_Port#Hardware_capability">EHCI
				Debug Port</a> ). Even more, if a USB controller supports EHCI debug, it
			is available only <b>on a single port</b> that might or might
			not be exposed externally.
		</p>
		<ul>
			<li>You need running OS (GNU/Linux) on your target for this step
				(If you&#8217;ve flashed libreboot and it does not boot, you have to
				flush back the stock bios)</li>
			<li>You need USB memory stick (the data on it will not be
				touched).</li>
			<li>The EHCI debugging can not be done through external hub, BBB
				must be connected directly to the debug port of the controller (so, no
				hubs)</li>
		</ul>
		<ul>
			<li>Download<sup class="footnote"><a href="#___fn1">1</a></sup> <a
				href="http://www.coreboot.org/pipermail/coreboot/attachments/20080909/ae11c291/attachment.sh">this</a>
				shell script.
			</li>
		</ul>
		<ol>
			<li>Plug the usb stick in the first available usb port</li>
			<li>Run the script, you will get output similar to following:</li>
<pre>The following PCI devices support a USB debug port (says lspci): 0000:00:1a.0 0000:00:1d.0
The following PCI devices support a USB debug port (says the kernel): 0000:00:1a.0 0000:00:1d.0
*PCI device 0000:00:1a.0, USB bus 3, USB physical port 1*
*PCI device 0000:00:1d.0, USB bus 4, USB physical port 2*
Currently connected high-speed devices:
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
	|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
		|__ Port 7: Dev 14, If 0, Class=Hub, Driver=hub/4p, 480M
			|__ Port 1: Dev 15, If 0, Class=Hub, Driver=hub/4p, 480M
			|__ Port 3: Dev 17, If 0, Class=Hub, Driver=hub/2p, 480M
			|__ Port 4: Dev 18, If 0, Class=Hub, Driver=hub/4p, 480M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
	|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M
/:  *Bus 01*.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
	|__ *Port 3: Dev 31, If 0, Class=Mass Storage, Driver=usb-storage, 480M*
</pre>
			<li>The buses the support debug are Bus 3 (0000:00:1a.0) on Port 1
				and Bus 4 (0000:00:1d.0) on port 2. Your usb stick is plugged on Bus
				1, Port 3</li>
			<li>Repeat the steps, plugging the USB stick in the next available
				port</li>
			<li>Go through all available ports and remember(write down) those
				for which bus/port of the usb stick matches one of the bus/port that
				support debug (bold).</li>
		</ol>
		<p>Remember (write down) for each port (external plug) you found
			that supports debug: <b>PCI device id, the bus id, the port number, and
			the physical location of the usb plug.</b></p>
		<p>If you do not find a match, you can not get debug over EHCI.
			Sorry.</p>
		<p id="___fn1" class="footnote">
			<sup>1</sup> The guys from coreboot were talking about including the
			script in coreboot distribution (check the status).
		</p>
		<h3 id="InitialsetupofBBBtoactasEHCIdebugdongle">Initial setup of
			BBB to act as EHCI debug dongle</h3>
		<p>BBB must be powered with a barrel power connector since the
			mini-B USB plug will be used for the EHCI debug stream. So you will
			need:</p>
		<ul>
			<li>power supply (5V, 2A(10W) is sufficient).</li>
			<li>an extra usb cable: A to mini-B</li>
		</ul>
		<p>
			(On BBB) The linux kernel includes module (g_dbgp that enables one of the usb ports on a computer to behave as EHCI
			debug dongle. Make sure you have this module available on your BBB
			(Debian 7.8 that comes with BBB should have it), if not, you should
			compile it yourself (see next section):
		</p>
<pre>ls /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget/g_dbgp.ko</pre>
	<p>
		Unload all other
		g_*
		modules:
	</p>
<pre># lsmod
# rmmod g_multi
...
</pre>
		<p>
			Then load
			g_dbgp
			:
		</p>
<pre># modprobe g_dbgp
# lsmod # should show that g_dbgp is loaded, and no other g_*
</pre>
		<p>
			Plug the mini-B side of the USB cable in your BBB and the A side in
			your target. Then one of the usb devices on your target (with
			lsusb
			) should be:
		</p>
<pre>Bus 001 Device 024: ID 0525:c0de Netchip Technology, Inc.</pre>
		<p>If you see the device on the target, you are good to continue to
			the next step.</p>
		<h3 id="PatchBBBsgdbgpmoduleoptionalbuthighlyrecommended">
			Patch BBB&#8217;s
			g_dbgp
			module (optional, but highly recommended)
		</h3>
		<p>
			For the reasons why you need this, see: <a
				href="http://www.coreboot.org/EHCI_Gadget_Debug">EHCI Gadget Debug</a>.<br />Make
			sure that you have cross compiling environment for
			arm-linux-gnueabihf
			setup on your <em>host</em>.
		</p>
		<ul>
			<li>On BBB: uname -r - this will give you version
				number like 3.8.13-bone70 (I will refer to this as: $mav.$miv-$lv:
				where mav=3.8, miv=13, lv=bone70
			</li>
			<li>Get the BBB kernel ready on your host for cross-compiling:</li>
		</ul>
<pre>$ cd $work_dir
$ git clone https://github.com/beagleboard/kernel.git
$ cd kernel
$ git checkout $mav (see above)
$ ./patch.sh
$ wget http://arago-project.org/git/projects/?p=am33x-cm3.git\;a=blob_plain\;f=bin/am335x-pm-firmware.bin\;hb=HEAD -O kernel/firmware/am335x-pm-firmware.bin
$ cp configs/beaglebone kernel/arch/arm/configs/beaglebone_defconfig
</pre>
		<ul>
			<li>Download the patch from <a
				href="http://www.coreboot.org/images/8/88/Ehci-debug-gadget-patches.tar.gz">here</a></li>
			<li>tar -xf Ehci-debug-gadget-patches.tar.gz (will
				create dir: usbdebug-gadget)</li>
			<li>Note that there are two patches (patch_1 and patch_2) for each
				of the two different version of the kernel (3.8 and 3.10). I will use
				3.8. (If using kernel 3.12 patch_1 is not needed)</li>
			<li>cd kernel (note that this is one more level: you
				should be in $work_dir/kernel/kernel)</li>
			<li>Apply the patches:</li>
		</ul>
<pre>
git apply ../usbdebug-gadget/v3.8-debug-gadget/0001-usb-dbgp-gadget-Fix-re-connecting-after-USB-disconne.patch
git apply ../usbdebug-gadget/v3.8-debug-gadget/0002-usb-serial-gadget-no-TTY-hangup-on-USB-disconnect-WI.patch
;
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- beaglebone_defconfig -j4@
</pre>
		<ul>
			<li>
				You should also apply the linux-libre <i>deblob</i> script to turn it into linux-libre
				(deletes all the blobs from the linux kernel).
				<a href="http://www.fsfla.org/ikiwiki/selibre/linux-libre/">fsfla website</a>
				- see <a href="http://www.fsfla.org/svn/fsfla/software/linux-libre/scripts/">scripts</a>.
			</li>
			<li>Get your current BBB kernel config (from: /boot/config-&lt;ver&gt;)
				and copy it to your host as $work_dir/kernel/kernel/.config</li>
<pre>
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- oldconfig - all default answers</pre>
			<li>Set proper version number:
				<ul>
					<li>On your host, edit $work_dir/kernel/kernel/.config
						(the one you&#8217;ve just copied from BBB), find the line CONFIG_LOCALVERSION="&lt;something
							or empty&gt;" and change it to CONFIG_LOCALVERSION="-$lv",
						so it will look something like: CONFIG_LOCALVERSION="-bone70"</li>
				</ul>
			</li>
			<li>Also, make sure that: CONFIG_USB_G_DBGP=m (If
				not, make menuconfig, and set @Device Drivers-&gt; USB
					Support -&gt; USB Gadget Support -&gt; EHCI Debug Device Gadget=m</li>
			<li>Build the module:</li>
		</ul>
<pre>
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j4 (is it possoble to build only the gadget modules)
$ mkdir ../tmp &amp;&amp; make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=../tmp modules_install
</pre>
		<ul>
			<li>on BBB, backup /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget
				(i.e. mv
					/lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget $HOME)
			</li>
			<li>copy the freshly compiled usb/gadget dir to /lib/modules/3.8.13-bone70/kernel/drivers/usb</li>
			<li>restart BBB</li>
			<li>Remove all g_* modules (rmmod
					g_&lt;&gt;)
			</li>
			<li>modprobpe g_dbgp</li>
		</ul>
		<h3 id="ConfigurelibrebootwithEHCIdebug">Configure libreboot with
			EHCI debug</h3>
		<p>
			Libreboot(coreboot) should be configured with debug turned on and to
			push debug messages to the EHCI debug port.<br />If you&#8217;ve
			downloaded the binary distribution, you can check if it is properly
			configured in the following way:
		</p>
		<ul>
			<li>Go to the libreboot dist root directory cd
					$libreboot_bin</li>
			<li>Locate the rom image for your target (I will call it: $img_path)
			</li>
			<li>Running the following command will extract the config in a
				file ./my_config:
			</li>
		</ul>
<pre>
./cbfstool/i686/cbfstool $img_path extract -n config -f ./my_config
</pre>
		<ul>
			<li>Make sure that the following params in the config are set as
				following:</li>
		</ul>
<pre>
CONFIG_USBDEBUG=y (Generic Drivers -&gt; USB 2.0 EHCI debug dongle support)
CONFIG_USBDEBUG_IN_ROMSTAGE=y (Generic Drivers -&gt; Enable early (pre-RAM) usbdebug)
CONFIG_USBDEBUG_HCD_INDEX=&lt;HCD Index of usb controller - see below&gt; (Generic Drivers -&gt; Index for EHCI controller to use with usbdebug)
CONFIG_USBDEBUG_DEFAULT_PORT=&lt;USB Debug port - see below&gt; (Generic Drivers -&gt; Default USB port to use as Debug Port)
</pre>
		<p>
			The following three are behind radio button in the menu. Only the first
			one<sup class="footnote"><a href="#___fn2">2</a></sup> should be =	y
		</p>
<pre>
USBDEBUG_DONGLE_STD=y                       (Generic Drivers -&gt; Type of dongle (Net20DC or compatible) -&gt; Net20DC or compatible)
CONFIG_USBDEBUG_DONGLE_BEAGLEBONE=n         (Generic Drivers -&gt; Type of dongle (Net20DC or compatible) -&gt; BeagleBone)
CONFIG_USBDEBUG_DONGLE_BEAGLEBONE_BLACK=n   (Generic Drivers -&gt; Type of dongle (Net20DC or compatible) -&gt; BeagleBone Black)
</pre>
		<p id="___fn2" class="footnote">
			<sup>2</sup> The g_dbgp	module on BeagleBone Black (Rev. C) reports it self as Net20DC, the
			other options are for older BB(B) - ver1. This is documented <a
				href="https://johnlewis.ie/coreboot-ehci-debug-gadget-demonstration/">here</a>
			(also tested/verified).
		</p>
		<p>
			Then:<br />
<pre>
CONFIG_CONSOLE_USB=y (Console -&gt; USB dongle console output)
</pre>
		</p>
		<p>
			Also
			Debugging ---&gt; Output verbose XYZ
			) (<b>FIXME</b> somebody verify these):
		</p>
<pre>
CONFIG_DEBUG_CBFS=y (Output verbose CBFS debug messages )
CONFIG_HAVE_DEBUG_RAM_SETUP=y (??? What/where is this)
CONFIG_DEBUG_RAM_SETUP=y (Output verbose RAM init debug messages)
CONFIG_DEBUG_SMI=y      (Output verbose SMI debug messages)
CONFIG_DEBUG_ACPI=y     (Output verbose ACPI debug messages )
CONFIG_DEBUG_USBDEBUG=y (Output verbose USB 2.0 EHCI debug dongle messages)
</pre>
		<p>If some of the above mentioned configuration options are not as
			specified, you have to configure and compile libreboot yourself. Please
			refer to the doc(<b>FIXME: link</b> about compiling libreboot.</p>
		<h4 id="SelectingHCDIndexandUSBDebugport">
			Selecting
			HCD Index
			and
			USB Debug port
		</h4>
		<p>
			This applies (and works) only if the USB controller that supports debug
			(found in the first section) is from Intel.<br />If the PCI ID of the
			port you found in the first section is
			0000:00:1a.0
			or
			0000:00:1d.0
			, you are ok. Otherwise you have to try without guarantee that will
			work.
		</p>
		<p>
			If the externally exposed port is on a bus with
			PCI ID == 0000:00:1a.0
			then for
			CONFIG_USBDEBUG_HCD_INDEX
			choose 2, otherwise choose 0
			.
		</p>
		<p>
			For
			CONFIG_USBDEBUG_DEFAULT_PORT
			choose the port from the first section that correspond to the
			PCI ID
		</p>
		<p>
			Notes:<br />The above is based on the implementation of
			coreboot/src/southbridge/intel/common/usb_debug.c : pci_ehci_dbg_dev()
			.<br />This is enough as it applies for the supported GM45/G45
			Thinkpads. coreboot support some other contollers too, but they are
			irellevent for libreboot (for now).
		</p>
		<ul>
			<li>On T500 (with switchable GPU) the debug ports for both intel
				controllers is exposed.</li>
			<li>On x200t the debug ports for both intel controllers is
				exposed.</li>
		</ul>
		<h3 id="Howtogetthedebuglogs">How to get the debug logs</h3>
		<ul>
			<li>Plug the USB cable in the target&#8217;s debug port (the one
				you found in step 1) and BBB&#8217;s mini-B USB</li>
			<li>Make sure no other then g_dbgp of the g_*
				modules is loaded on your BBB
			</li>
			<li>On the BBB:</li>
		</ul>
<pre>
stty -icrnl -inlcr -F /dev/ttyGS0
cat /dev/ttyGS0
</pre>
		<ul>
			<li>Power on the target with libreboot</li>
			<li>You should see debug logs comming on your BBB console</li>
		</ul>
		<p>
			Note that this is not permanent on BBB, if you reboot it, you have to
			rmmod g_*
			and
			modprobe g_dbgp
		</p>
		<h3 id="EnebleEHCIDebugonthetargetskerneloptionalrecommended">Eneble
			EHCI Debug on the target&#8217;s kernel (optional, recommended)</h3>
		<p>You have to know how to compile kernel for your target.</p>
		<ol>
			<li>Check if early debugging is already enabled: grep
					CONFIG_EARLY_PRINTK_DBGP /boot/config-&lt;ver&gt;</li>
			<li>If enabled, you do not have to compile the kernel (skip this
				step). Otherwise, prepare kernel source for your distribution and
				select (Kernel hacking -&gt; Early printk via EHCI debug
					port). Compile and install the new kernel.
			</li>
			<li>Edit your grub configuration and add following to the kenel
				parameters<sup class="footnote"><a href="#___fn20">20</a></sup><sup
				class="footnote"><a href="#___fn21">21</a></sup>: earlyprintk=dbgp,keep.
				Also, try: earlyprintk=dbgp&lt;N&gt;,keep where N
				is the debug port id if the first does not work.
			</li>
		</ol>
		<h3 id="References">References</h3>
		<p id="___fn10" class="footnote">
			<sup>10</sup> <a href="http://www.coreboot.org/EHCI_Debug_Port">EHCI
				Debug Port</a>
		</p>
		<p id="___fn11" class="footnote">
			<sup>11</sup> <a
				href="https://johnlewis.ie/coreboot-ehci-debug-gadget-demonstration/">coreboot
				EHCI debug gadget demonstration</a>
		</p>
		<p id="___fn12" class="footnote">
			<sup>12</sup> <a href="http://www.coreboot.org/EHCI_Gadget_Debug">EHCI
				Gadget Debug</a>
		</p>
		<p id="___fn13" class="footnote">
			<sup>13</sup> <a
				href="http://www.coreboot.org/images/8/88/Ehci-debug-gadget-patches.tar.gz">Ehci-debug-gadget-patches.tar.gz</a>
		</p>
		<p id="___fn14" class="footnote">
			<sup>14</sup> <a
				href="http://wiki.beyondlogic.org/index.php/BeagleBoneBlack_Building_Kernel">Compiling
				the BeagleBone Black Kernel</a>
		</p>
		<p id="___fn15" class="footnote">
			<sup>15</sup>
			http://dumb-looks-free.blogspot.ca/2014/06/beaglebone-black-bbb-compile-kernel.html
		</p>
		<p id="___fn16" class="footnote">
			<sup>16</sup>
			http://dumb-looks-free.blogspot.fr/2014/06/beaglebone-black-bbb-kernal-headers.html
		</p>
		<p id="___fn17" class="footnote">
			<sup>17</sup> <a href="http://elinux.org/Building_BBB_Kernel">Building
				BBB Kernel</a>
		</p>
		<p id="___fn18" class="footnote">
			<sup>18</sup>
			http://komposter.com.ua/documents/USB-2.0-Debug-Port%28John-Keys%29.pdf
		</p>
		<p id="___fn19" class="footnote">
			<sup>19</sup> <a href="http://cs.usfca.edu/~cruse/cs698s10/">Exploring
				USB at the Hardware/Software Interface</a>
		</p>
		<p id="___fn20" class="footnote">
			<sup>20</sup>
			https://www.kernel.org/doc/Documentation/x86/earlyprintk.txt
		</p>
		<p id="___fn21" class="footnote">
			<sup>21</sup> https://wiki.ubuntu.com/Kernel/Debugging/USBearlyprintk
		</p>
		<p>
			<b>TODO</b>:
		</p>
		<ol>
			<li>grub does not send messages to EHCI debug. Investigate.</li>
			<li>The section &#8220;Configure libreboot with EHCI debug&#8221;
				can be skipped/simplified if a common configuration works for all
				relevant targets is selected as defualt</li>
			<li>Patch and compule g_dbgp on BBB instead cross-compile</li>
			<li>Find a simple way to send debug messages from targets userland</li>
		</ol>
	</div>

	<div class="section">

		<p>
			Copyright &copy; 2015 Alex David &lt;opdecirkel@gmail.com&gt;<br/>
			Permission is granted to copy, distribute and/or modify this document
			under the terms of the GNU Free Documentation License, Version 1.3
			or any later version published by the Free Software Foundation;
			with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
			A copy of the license can be found at <a href="../gfdl-1.3.txt">../gfdl-1.3.txt</a>
		</p>

		<p>
			Updated versions of the license (when available) can be found at
			<a href="https://www.gnu.org/licenses/licenses.html">https://www.gnu.org/licenses/licenses.html</a>
		</p>

		<p>
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			The disclaimer of warranties and limitation of liability provided
			above shall be interpreted in a manner that, to the extent
			possible, most closely approximates an absolute disclaimer and
			waiver of all liability.
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